1. Field of the Invention
The present invention relates to hydraulic lash adjusters used in valve trains of internal combustion engines and more particularly to a self-contained hydraulic lash adjuster in which the fluid is sealed within the assembly with no provision for its replenishment from any external source during operation.
2. Prior Art
In the valve trains of internal combustion engines predetermined valve clearances are generally provided in order to compensate for thermal expansion of various parts in the valve trains. However, since excess lash may be generated due to the valve clearances in the valve trains during engine operation, hydraulic lash adjusters have been used for automatically taking up the valve clearances in the valve trains thereby preventing any possible lash in stabilizing the opening and closing operation of the engine intake or exhaust valves.
Conventional hydraulic lash adjusters compensate for fluid leakage by means of supplying pressurized fluid to the interior of the lash adjusters through passageways in the cylinder block. However, there are disadvantages to such an arrangement since the passageways through which the pressurized fluid flows are complicated in construction and the operation is often unstable due to changes in the viscosity of the pressurized fluid. In order to eliminate such disadvantages hydraulic lash adjusters of the self-contained type have been provided which are not fed from an external source of hydraulic fluid but contain their own source of such fluid.
In conventional hydraulic lash adjusters of the self-contained type there are still drawbacks since the mechanism compensating for fluid leakage is often imperfect, the operation might become unstable due to the entrapment of air in the fluid and the mechanism of the lash adjuster is quite complicated and expensive to manufacture.
An example of a self-contained hydraulic lash adjuster is disclosed in the Kodama U.S. Pat. No. 4,191,142. The selfcontained lash adjuster disclosed in the Kodama patent includes a cylinder member and a plunger member slidably fitted therein to define a fluid pressure chamber between each end wall. The plunger member is provided with a reservoir chamber therein and an elastic bag member is disposed within the reservoir chamber with the inner wall surface of the elastic bag member being normally in communication with atmospheric pressure while the outer wall surface thereof is disposed in contact with the fluid in the reservoir chamber.